The present invention relates to an illuminating device, and more particularly to an illuminating device for uniformly illuminating a planar object.
Paintings, for example, are required to be uniformly illuminated when they are displayed.
For uniformly exposing a planar photosensitive surface in a full-exposure electrophotographic or electrostatic copying machine, the surface of an original document to be copied is illuminated at a special distribution of light intensities in view of the cosine law of a focusing lens. If the entire surface of the original document can be uniformly illuminated, it is far easier and more accurate to correct exposure light rays for achieving a uniform exposure condition than to accomplish the special light intensity distribution.
Therefore, uniform illumination of a planar object is of great technical merit in various fields.
One known method of uniformly illuminating a planar object in relation to an electrophotographic copying machine is disclosed in U.S. Pat. No. 4,298,275. According to the disclosed method, light emitted from a light source is diffused in order to illuminate the object. However, the method as it is used to illuminate an original document in a copying machine is problematic in that it produces a large amount of flaring. Another problem with this method is that much difficulty would be experienced in applying the method to other fields than the electrophotographic copying machine.